Born in Boston, MA on March 5, 1968, David Creegan was a normal, straight-laced FBI agent with a wife, Holly, and two daughters, Lily and Samantha. Settling in San Fransico, David, among the best in his field, is choosen to be one of the founding members of a elite unit within the FBI called the OSC- Organized And Serial Crimes Unit. A man with a bright and prosmising future until one day while searching a house for a criminal, he is shot twice- once in the head. He is pronouced dead at the hospitial but ten minutes later, comes back.
The man he comes back as, though, is not the man he died as. In order to remove the bullet from his brain, doctors have to actually remove part of David's brain. They find out later that the section they removed was the area which governers shame. Things go from bad to worse when David's mental state deteriorates. He can no longer feel the love he once did for his wife and children- a wall comes down between them and him. Without the love, he feels no connection to them and this leads to divorce. David slips more and more towards mania and, eventually, looses his grip on reality and finds him in a very dark place where he sees the only way to be suicide. He is sent to a mental hospitial and a year later, thanks to the caring staff there, is able to pull out of his depression. It takes a long time, but three years after he dies, he is finally able to return to his job at the OSC where he is partnered with Detective Inspector Susan Branca.
Branca is not all that happy about being matched up with Creegan at first. She believes him to still be in a questionable mental state and tells Captain Hank Enright her opinion. Enright, who was helped David form the OSC three years ago understands her concerns but is determined to help his old friend if he can. In the end, Branca is forced to put up with Creegan's oddities and become a loyal partner to him.
As time has gone by, Brance seems to have come to accept the fact that her partner is not normal and will never be normal. Creegan relies on her to help him see the world because his brain injury has also left him with a sequencing problem and damage to his parifiral vision. Creegan can be himself with Branca because she has no normal expectations of him. She did not know him before he died so she has no idea what kind of person he was. She only knows him as he is now. In turn, Creegan encourages Branca to not bottle up all her pain and emotions- he wills her not to loose herself as she tries to keep the job from getting to her. They understand and relate to each other, leading them to being more than parteners- they are friends. Together, Creegan and Branca track down the some of the world's most evil and notorious killers.
Within the OSC, David has other allies. Jay Swopes is probably the most notable of these. Though most write off Swopes' social awkawardness as stupidity, David can see an intelligent and gifted man who wants to belong to the group. David is always the first to treat Swopes as one of the "guys" and not just a circus freak. For this, Swopes is grateful and is always willing to do odd-jobs for David. They seem to understand one another without even speaking.
While almost everyone in the OSC comes to respect and like David, there is one who resents him- Charles "Chas" Bernal. Always, one to point out mistakes and poke fun at other's short-comings, Bernal enjoys being the best. When David comes along and turns out to be better and more gifted than him, Bernal can't stand it. The tension has risen so high that once it came to blows at the OSC three year anniversary party. Bernal wants to upstage Creegan so badly, it hurts but, for now, it seems he is destined to walk in his revial's shadow.
In a weird turn of events during the "Pilot" David comes to have another friend, Cryil Kemp. Cryil is an out of work substitute teacher who suffers from neurological problems and, as a result, believes he is from a space station called, "Alpha 9". He starts out as a suspect in the kidnapping of three boys. When he is finally cleared he has no place to stay and no money so David takes him to the same mental hospitial that treated him. Cryil is released and comes to live with David in his motel room. This does not last long as Cryril stops taking his medication and, with David's help and guidance, is sent to another hospitial. Hopefully, someday he can return to his friend, David.
David's relationship with his family is slowly getting better. After sending them into witness protection, Enright returns them to him and, now, David, is starting to find his way back to his daughters. His relationship with Holly, though, seems destined to distance as she still wants him to be the man he once was. If she can ever find a way to accept who he is now, perhaps someday, they can find each other again.

"You know, someone once said, 'Life is the illusion.' I disagree. Death is the illusion... This... This is real."~David Creegan, 'Mercy'